Analyses using microbial cells or other biological specimens have been performed, for example, by inoculating microbes on an agar medium and observing them by the naked eye after they are maintained for a certain period of time at a constant temperature in an incubator. In recent years, however, liquid culture has become more popular, which employs a multiwell plate having a plurality of wells. Moreover, for chemical reactions involved in, for example, combinatorial chemistry, multiwell plates are often used to perform analysis of many specimens.
Usually, the above-mentioned liquid culture and specimen analyses are performed as follows: Specimens are added to the wells of a multiwell plate and cultured while maintained at a predetermined temperature for a predetermined period of time, followed by irradiation with light. Subsequently, transmitted light or scattering light including fluorescence is measured.
Hitherto, for maintaining a temperature of a multiwell plate, the plate is typically placed on a flat heat-retentive plate. Also, in practice of retaining temperature of a multiwell plate, an incubation apparatus having shelves provided with such heat-retentive plates is employed (see Patent Document 1).
However, when incubation is performed under a variety of different temperature conditions, intricate manipulation is required. That is, an incubation apparatus must be provided for each temperature, and multiwell plates must be placed in a plurality of incubation apparatuses, each of which has been set at a specific temperature.
Moreover, for performing analyses, the multiwell plates must be taken out of the incubation apparatuses, which is also inconvenient.
In order to solve these problems, there has been proposed a so-called continuous temperature-gradient incubation apparatus, which employs a heat-conductive container having a plurality of orderly arranged wells, wherein one end of the container is set at a high temperature and the other end is set at a low temperature (see Patent Documents 2 to 4).                [Patent Document 1] JP-A 2003-289848        [Patent Document 2] WO90/10689        [Patent Document 3] EP-A 0290722        [Patent Document 4] U.S. Pat. No. 4,865,987        